MSE veterans won't notice a lot of huge changes in this version, but certain interface elements have changed slightly—the icons along the top are gone, and certain wordings have changed a bit to make the program easier to use. The "Real-Time Protection" setting is now an all-or-nothing checkbox, and SpyNet has been renamed to the Microsoft Active Protection Service to make a bit clearer what it actually does. Microsoft has also baked in some performance improvements and better detection powers.

Microsoft Security Essentials is a free download for Windows only. You can get the new version through Windows Update, or on its home page at the link below.